Operators of small internal combustion engines, such as one and two cycle, four stroke engines, often fail to adequately maintain the necessary level of lubricating oil in the crankcase resulting in failure of the engine. It is therefore desirable to have a protective system built into the engine which will either shut down operation of the engine, or operate a visual or audio signal should the oil level fall to a dangerously low level.
With a splash lubricated engine, an automotive-type oil pressure switch cannot be utilized. In the past, various types of mechanical systems have been proposed for use with splash lubrication systems to detect a dangerously low lubricating oil level. The detecting mechanisms, as used in the past have, for example, included float switches, capacitor switches, and thermal switches. Float switches are rather large and difficult to adapt to existing equipment and due to the substantial number of moving parts are not completely failsafe. Capacitance and thermal switches generally are quite costly and require an external power supply for operation.
More recently, low level lubricating oil detectors, which operate on pressure pulsations produced by the engine, have been proposed, as disclosed in U.S. Pat. No. 4,203,408. With this type of system, an oil detecting tube extends into the crankcase of the engine and has an opening which is located at the predetermind minimum oil level. The outer end of the tube is connected to an external chamber enclosed by a diaphragm-type actuator and a check valve is located in the tube adjacent the chamber. When the oil level recedes below the predetermined minimum level, the pressure pulsations in the crankcase are transmitted through the tube and the check valve allows pressure to build up in the chamber to thereby flex the diaphragm. Flexing of the diaphragm operates through a mechanical linkage to operate a switch to stop operation of the engine. However, detecting systems operating on pressure pulsations as disclosed in U.S. Pat. No. 4,203,408, are relatively complex and due to the large number of moving parts, which can stick, wear, or break, do not offer a completely failsafe operation.